This invention relates to infrared detectors and, more particularly, to an infrared detector which includes an infrared sensor such as a pyroelectric element generating a voltage upon incident of infrared rays, for detecting the infrared rays originating from an object to be detected as condensed by a Fresnel lens.
Because the infrared detector of the type referred to performs its detecting operation in response to incident infrared rays originating, for example, from human bodies, the detector can be effectively utilized in such systems that are for supervising any intruder into a building or the like where the detector is installed to inform it, and the like purposes.